Upshot-Knothole Grable was a nuclear weapons test

Nuclear testing

Nuclear weapons tests are experiments carried out to determine the effectiveness, yield and explosive capability of nuclear weapons. Throughout the twentieth century, most nations that have developed nuclear weapons have tested them...

 conducted by the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 as part of Operation Upshot-Knothole

Operation Upshot-Knothole

Operation Upshot-Knothole was a series of eleven nuclear test shots conducted in 1953 at the Nevada Test Site.Over twenty-one thousand soldiers took part in the ground exercise Desert Rock V in conjunction with the Grable shot...

. Detonation of the associated nuclear weapon

Nuclear weapon

A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...

 occurred shortly after its deployment at 8:30am PDT

Pacific Time Zone

The Pacific Time Zone observes standard time by subtracting eight hours from Coordinated Universal Time . The clock time in this zone is based on the mean solar time of the 120th meridian west of the Greenwich Observatory. During daylight saving time, its time offset is UTC-7.In the United States...

 (1530 UTC

Coordinated Universal Time

Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...

) on May 25, 1953, in Area 5 of the Nevada Test Site

Nevada Test Site

The Nevada National Security Site , previously the Nevada Test Site , is a United States Department of Energy reservation located in southeastern Nye County, Nevada, about northwest of the city of Las Vegas...

. The codename Grable was chosen because the letter Grable is phonetic for, G, stands for "gun", since the warhead was a gun-type fission weapon

Gun-type fission weapon

Gun-type fission weapons are fission-based nuclear weapons whose design assembles their fissile material into a supercritical mass by the use of the "gun" method: shooting one piece of sub-critical material into another...

. It was in the form of a shell, or artillery-fired atomic projectile

Nuclear artillery

Nuclear artillery is a subset of limited-yield tactical nuclear weapons, in particular those weapons that are launched from the ground at battlefield targets...

 (AFAP), the first of its kind.

Grable was the second of only two gun-type warheads ever detonated (the first was Little Boy

Little Boy

"Little Boy" was the codename of the atomic bomb dropped on Hiroshima on August 6, 1945 by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul Tibbets of the 393rd Bombardment Squadron, Heavy, of the United States Army Air Forces. It was the first atomic bomb to be used as a weapon...

, the weapon used against Hiroshima

Hiroshima

is the capital of Hiroshima Prefecture, and the largest city in the Chūgoku region of western Honshu, the largest island of Japan. It became best known as the first city in history to be destroyed by a nuclear weapon when the United States Army Air Forces dropped an atomic bomb on it at 8:15 A.M...

; all other atomic weapons were implosion-type weapons). The shell, designated a Mark 9

W9 (nuclear warhead)

The W9 was an American nuclear artillery shell fired from a special 11 inch howitzer. It was produced starting in 1952 and all were retired by 1957.-Description:...

 nuclear weapon, had a diameter of 280 mm (11.02 in), was 138 cm (54.4 in) long and weighed 364 kg (803 lb). The M65 Atomic Cannon

M65 Atomic Cannon

The M65 Atomic Cannon, often called Atomic Annie, was a towed artillery piece built by the United States and capable of firing a nuclear device. It was developed in the early 1950s, at the beginning of the Cold War, and fielded by 1953 in Europe and Korea....

 from which it was fired had a muzzle velocity of 625 m/s (2,060 ft/s), for a nominal range of 32 km (19.9 mi), and weighed 77 metric tons

Tonne

The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

 (85 t

Short ton

The short ton is a unit of mass equal to . In the United States it is often called simply ton without distinguishing it from the metric ton or the long ton ; rather, the other two are specifically noted. There are, however, some U.S...

).

The detonation of Grable occurred 19 seconds after its firing. It detonated over 11,000 yards (over 10 km, 6.25 mi) away from the gun it was fired from, over a part of the Nevada Test Site known as Frenchman Flat

Frenchman Flat

Frenchman Flat is a Tonopah Basin landform used as a nuclear weapons detonation site at the Nevada Test Site , some from Las Vegas, in the United States. Frenchman Flat is a dry lake, an alkaline desert depression which spans Area 5 and Area 11 within NTS...

. The explosion was an air burst

Air burst

An air burst is the detonation of an explosive device such as an anti-personnel artillery shell or a nuclear weapon in the air instead of on contact with the ground or target or a delayed armor piercing explosion....

 of 160 m (524 ft) above the ground (7 m (24 ft) above its designated burst altitude), 26 m (87 ft) west and 41 m (136 ft) south of its target (slightly uprange). Its yield was estimated at 15 kilotons

TNT equivalent

TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...

, around the same level as Little Boy

Little Boy

"Little Boy" was the codename of the atomic bomb dropped on Hiroshima on August 6, 1945 by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul Tibbets of the 393rd Bombardment Squadron, Heavy, of the United States Army Air Forces. It was the first atomic bomb to be used as a weapon...

. An anomalous feature of the blast was the formation of a precursor

Precursor (physics)

Precursors are characteristic wave patterns caused by dispersion of an impulse's frequency components as it propagates through a medium. Classically, precursors precede the main signal, although in certain situations they may also follow it...

, a second shock front ahead of the incident wave. This precursor was formed when the shock wave

Shock wave

A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...

 reflected off the ground and surpassed the incident wave and Mach stem due to a heated ground air layer and the low burst height. It resulted in a lower overpressure, but higher overall dynamic pressure, which inflicted much more damage on drag

Drag (physics)

In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

 sensitive targets such as jeeps and personnel carriers. This led strategists to rethink the importance of low air bursts in tactical nuclear warfare

Nuclear warfare

Nuclear warfare, or atomic warfare, is a military conflict or political strategy in which nuclear weaponry is detonated on an opponent. Compared to conventional warfare, nuclear warfare can be vastly more destructive in range and extent of damage...

.

Some images from Upshot-Knothole Grable were accidentally relabeled as belonging to the Priscilla shot from Operation Plumbbob

Operation Plumbbob

Operation Plumbbob was a series of nuclear tests conducted between May 28 and October 7, 1957, at the Nevada Test Site, following Operation Redwing, and preceding Operation Hardtack I...

 in 1957. As a consequence many publications including official government documents have the photo mislabeled.

Admiral Arthur W. Radford

Arthur W. Radford

Arthur William Radford was a United States Navy Admiral, Commander-in-Chief of the United States Pacific Command and Chairman of the Joint Chiefs of Staff.Arthur Radford was born in Chicago, Illinois, in 1896...

, at the time the Chairman of the Joint Chiefs of Staff

Chairman of the Joint Chiefs of Staff

The Chairman of the Joint Chiefs of Staff is by law the highest ranking military officer in the United States Armed Forces, and is the principal military adviser to the President of the United States, the National Security Council, the Homeland Security Council and the Secretary of Defense...

, and Secretary of Defense

United States Secretary of Defense

The Secretary of Defense is the head and chief executive officer of the Department of Defense of the United States of America. This position corresponds to what is generally known as a Defense Minister in other countries...

 Charles E. Wilson

Charles Erwin Wilson

Charles Erwin Wilson , American businessman and politician, was United States Secretary of Defense from 1953 to 1957 under President Eisenhower. Known as "Engine Charlie", he previously worked as CEO for General Motors. In the wake of the Korean War, he cut the defense budget significantly.-Early...

were present for the test.

External links

• Video clip of Grable nuclear artillery experiment
• The Atomic Cannon from AtomCentral.com, including video.